1. Field of the Invention
The present invention generally relates to an information processing apparatus and a method of controlling the same. More specifically, the present invention relates to an information processing apparatus using a liquid crystal display panel as an output device and a resistance film type touch panel as an input device, and a method of controlling the same.
2. Background Information
In recent years, small size portable personal computers having a touch panel combined with a liquid crystal display panel, which may be represented by a PDA (personal digital assistant), are widely available for practical use.
A type of liquid crystal display panel can be categorized to a simple matrix system represented by an STN (super twisted nematic), an active matrix system represented by a TFT (thin film transistor), etc. according to the drive system. In either type, however, in order to prevent degradation of the characteristics of a liquid crystal that could happen when direct current (DC) voltage is impressed for a long time, reverse drive is conducted at a certain fixed cycles for switching the polarity of a voltage that drives the liquid crystal.
Moreover, a type of touch panel can be categorized as a resistance film type, an electrostatic capacity type, an optical type, an ultrasonic type, etc. according to the principle of operation. Among these types, especially the resistance film type can be applied in small size and be acquired at low cost, and therefore, it has been widely used as an input device for a portable personal computer.
FIG. 1 shows a conventional information processing apparatus 1002 where a resistance film type touch panel is combined with a liquid crystal display panel. The information processing apparatus 1002 is provided with an MPU (micro processing unit) 100, a liquid crystal display panel control circuit 200, a liquid crystal display panel 300, a resistance film type touch panel control circuit 400, and a resistance film type touch panel 500.
The MPU 100 is connected with the liquid crystal display panel control circuit 200 and the resistance film type touch panel control circuit 400 through a system bus, and manages to control the entire information processing apparatus 1002. In this structure, the liquid crystal display panel control circuit 200 controls the liquid crystal display panel 300 based on the commands from the MPU 100, and the resistance film type touch panel control circuit 400 controls the resistance film type touch panel 500 based on the commands from the MPU 100.
The liquid crystal display panel control circuit 200 is provided inside with a horizontal synchronizing signal generating circuit 201 and an alternating current (AC) signal generating circuit 202. A horizontal synchronizing signal S1 generated by the horizontal synchronizing signal generating circuit 201 is first inputted to the liquid crystal display panel 300. One pulse of the horizontal synchronizing signal S1 is equivalent to one scanning line of the liquid crystal display panel 300.
The horizontal synchronizing signal S1 is also inputted to the alternating current signal generating circuit 202. The alternating current signal generating circuit 202 generates an alternating current signal S2 for reversing the polarity of a liquid crystal drive voltage based on the horizontal synchronizing signal S1. In concrete terms, the alternating current signal generating circuit 202 has a divider inside, and the divider divides (i.e. multiplies by 1/n) the frequency of the horizontal synchronizing signal S1 into a desired frequency. Accordingly, the alternating current signal S2 is generated.
Since one pulse of the horizontal synchronizing signal S1 is equivalent to one scanning line of the liquid crystal display panel 300 as mentioned above, when the alternating current signal S2 is generated by dividing the horizontal synchronizing signal S1 by ‘n’, for example, n scanning lines will simultaneously be subjected to a reverse drive by this alternating current signal S2. The frequency division ratio ‘n’, for instance, is set up at an internal register of the alternating current signal generating circuit 202 by software. In FIG. 1, for the sake of convenience, only some of the signals exchanged between the liquid crystal display panel control circuit 200 and the liquid crystal display panel 300 are shown.
The resistance film type touch panel 500 includes, for example, an upper film and a lower film where a conductive substance such as an ITO (indium tin oxide) film is formed at each opposing surface. There is a certain or predetermined spacing between the upper film and the lower film, and by pressing the upper or lower film with a finger, or a pen, etc., the upper film and the lower film can make contact with each other and conduct current.
The upper film and the lower film are respectively provided with electrodes whose directions are opposite from each other. For instance, the upper film has the electrode along the X-axis direction and the lower film has the electrode along the Y-axis direction. Voltage is impressed independently to each electrode.
When the resistance film type touch panel 500 is pressed, the impressed voltage will be divided by resistance depending on the pressed position, and the resistance-divided voltage will be outputted to the resistance film type touch panel control circuit 400 as a coordinate detection voltage S4.
The coordinate detection voltage S4 is supposed to be outputted independently from the X-axis coordinate and the Y-axis coordinate, but in this particular case, for the sake of convenience, the coordinate detection voltages S4 of the X-axis coordinate and the Y-axis coordinate will not especially be distinguished.
Based on the commands from the MPU 100, the resistance film type touch panel control circuit 400 samples the coordinate detection voltage S4 for a certain period of time and collects position coordinate data, which point out the pressed positions in the resistance film type touch panel 500. In FIG. 1, for the sake of convenience, only some of the signals exchanged between the resistance film type touch panel control circuit 400 and the resistance film type touch panel 500 are shown.
For example, an input device using a touch panel is indicated by Japanese Patent Application Laid-Open No. 10-40016 (hereinafter reference 1), especially pp. 2-3, FIGS. 1 and 4. Japanese Patent Application Laid-Open No. 10-40016 is hereby incorporated by reference. The touch panel input device given in the reference 1 includes a resistance film type touch panel having a film for detecting the X-axis coordinate and a film for detecting the Y-axis coordinate. The touch panel input device of the reference 1 further includes a means to avoid incorrect detection of position coordinates due to possible bending of the film in the resistance film type touch panel, and possible noises from a liquid crystal display panel and a CRT (cathode ray tube), which are put by the side of the touch panel input device.
Generally, a touch panel is used as a direct input device with respect to a display, and is attached close to the front of a liquid crystal display panel and such. As described above, in the liquid crystal display panel, the liquid crystal drive voltage is reversed at a certain fixed cycle. However, when the liquid crystal drive voltage is reversed, radiation noise is generated from the liquid crystal display panel and superimposed on a coordinate detection voltage of the adjacent touch panel. This causes an incorrect detection of position coordinates.
With respect to the structure of the information processing apparatus 1002 shown in FIG. 1, there is a problem, as just mentioned, that the position coordinates in the resistance film type touch panel 500 is detected incorrectly due to the radiation noise generated at the time the polarity of the liquid crystal drive voltage is reversed.
FIG. 2 shows the influence of the radiation noise over the coordinate detection in the resistance film type touch panel 500. Generally, the touch panel 500 is used in a state being attached close to the front of the liquid crystal display panel 300. In the liquid crystal display panel 300, the polarity of the liquid crystal drive voltage is reversed at a certain fixed cycle according to the alternating current signal S2. When the drive voltage is reversed, i.e. when the level of the alternating current signal S2 changes (i.e. from High level to Low level or from Low level to High level), radiation noise S4a is generated from the liquid crystal display panel 300. As shown in FIG. 2, the radiation noise S4a is superimposed on the coordinate detection voltage S4 from the resistance film type touch panel 500, and induces incorrect detection of position coordinates.
FIG. 3 is a time chart of the signals in the information processing apparatus 1002. One pulse of the horizontal synchronizing signal S1 is equivalent to one scanning line of the liquid crystal display panel 300. The alternating current signal S2 is generated by dividing the horizontal synchronizing signal S1. For instance, the alternating current signal S2 shown in FIG. 3 is generated by dividing the horizontal synchronizing signal S1 by six. The coordinate detection voltage S4 is position coordinate data with respect to the resistance film type touch panel 500. Sampling of the coordinate detection voltage S4 is repeatedly conducted for a certain period of time and asynchronously with the horizontal synchronizing signal S1 and the alternating current signal S2.
As described with reference to FIG. 2, a radiation noise may be generated at level changing intervals of the alternating current signal S2 (shown by arrows). When the level changing interval of the alternating current signal S2 and the sampling interval of the coordinate detection voltage S4 coincides with each other, as can be noted by the sampling interval indicated by arrow A in FIG. 3 for example, the radiation noise S4a will be superimposed on the waveform of the coordinate detection voltage S4 and change the original signal waveform.
In order to remove noise, the touch panel input device disclosed in the reference 1 detects coordinate data more than once with respect to each of the X-axis coordinate and the Y-axis coordinate, and determines the presence of noise by comparing the detected multiple coordinate data.
This noise removal method is noted as very effective in removing noises that are generated irregularly. However, this method is not effective in removing noises that are generated at a certain fixed cycle, as the radiation noise accompanied by the reversal of the liquid crystal drive voltage. In other words, this method is not effective in removing noises whose occurrence can be predicted in advance, because the processing time becomes redundant.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved information processing apparatus and an improved method of controlling an information processing apparatus. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.